At the photo-engraving process in the field of print-duplicating, a photographic image having continuous gradation is converted into a dot image, in which the density of the image is represented in terms of the dot area, and a print manuscript is prepared by combining together the dot image and a manuscript containing figures and lines.
In order to improve reproduction of line and dot images, the light-sensitive material used in photo-engraving process must have ultra-high contrast photographic characteristics (in particular, a .gamma. of 10 or more), i.e., sufficiently high image contrast to clearly distinguish an image area from a non-image area, and high blackening density. Thus it is required to develop an image-forming system satisfying such requirements.
For this purpose, a method has generally been employed in which a lith-type silver halide light-sensitive material containing silver chlorobromide with 40 mol% or less of silver bromide is processed with a hydroquinone developer (lith developer) in which the effective concentration of sulfite ions is very low (usually 0.1 mol/l or less). In this method, however, the developer is extremely unstable against air oxidation because the concentration of sulfite ions in the developer is low.
An image-forming system is desired that overcoming the instability in formation of images due to the lith developer and provides ultra-high contrast photographic characteristics using a processing solution having good storage stability. U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, 4,311,781 disclose a system for forming negative images of ultra-high contrast (i.e., a .gamma. in excess of 10) by processing a surface latent image-type silver halide photographic material containing a specific acylhydrazine compound at a pH of 10.5 to 12.3 with a developer of good storage stability, containing 0.15 mol/l or more of a sulfite preservative. This image-forming system permits the use of silver iodobromide or silver chloroiodobromide of high sensitivity, while on the other hand, in the conventional method of formation of ultra-high contrast images, only silver chloride or silver chlorobromide can be used.
Further, Japanese Patent Application (OPI) No. 68419/77 (the term "OPI" as used herein means a "published unexamined Japanese Patent Application") also discloses the system for forming negative image though there is no discription about a light-sensitive material having an ultra-high contrast by using hydrazine derivatives.
It is necessary for the dot images, or line and figure images formed by the above image-forming system to have good printability (i.e., such property that a demanded quality of finale prints such as color density, color balance, and line width of line image is satisfied). For this printability, the silver image must often be corrected. For this correction of silver images, a reduction method is employed in which by contacting the silver image with a reducing solution, the blackened area of dots is reduced and the line and figure images are corrected.
The reduction is to dissolve a silver image through oxidation. Therefore, by reduction the density of the silver image is decreased. The "effective reduction width" is the extent to which the area of the silver image can be reduced in relation to the original area when the density of the silver image is lowered to the very limited necessary value for the photo-engraving (for example, a transmission optical density of 2.5).
In connection with reduction, many studies have been made, including those described in Japanese Patent Application (OPI) Nos. 140733/76, 68419/77, 119236/79, 119237/79, 2244/80, and 2245/80 (the term "OPI" as used herein means a "published unexamined Japanese patent application"). In these methods, a reducing solution containing red prussiate (i.e., potassium ferricyanide) as a major component has been used. This reducing solution, however, is subjected to environmental regulation due to its pollution of waste water and, therefore, cannot be used without expensive waste water treatment. For this reason, a reducing solution containing a cerium (IV) salt as a major component has been used in recent years.
If, however, a silver image formed by processing a surface latent image-type silver halide photographic material containing an acylhydrazine compound as described above with a developer containing 0.15 mol/l or more of a sulfite preservative and adjusted to pH 10.5 to 12.3 is treated with a reducing solution containing a cerium (IV) salt as a major component, a problem arises in that a yellow-brown residue is formed around the reduced silver image and the effective reduction width is reduced.
If the above residue has an optical density above a certain limit, it functions as a component constituting the image and, therefore, undesirably decreases the effective reduction width.